A liquid crystal display panel including a thin film transistor using amorphous silicon as a driving element of liquid crystal is widely used in commercial products such as a monitor of a computer and a liquid crystal television. A manufacturing technique of a thin film transistor using amorphous silicon is already established and a liquid crystal panel with more than 60 inches has been produced.
Since operation speed of a thin film transistor using amorphous silicon is slow and any further high performance cannot be expected, a thin film transistor using polysilicon has been developed. However, a crystallization step is required for making polysilicon, which leads to cause variation in transistor characteristics or inhibit enlargement of a panel area.
In contrast, an oxide semiconductor material has been attracting attention as a transistor material besides a silicon based material. As an oxide semiconductor material, zinc oxide or a substance containing zinc oxide is known. Thin film transistors each of which is formed using an amorphous oxide (an oxide semiconductor) having an electron carrier concentration of lower than 1018/cm3 are disclosed (see Patent Documents 1 to 3).
Liquid crystal display devices are widely used for display devices ranging from large-sized display devices such as television sets to small-sized display devices such as mobile phones. Therefore, the development of liquid crystal display devices is intended to achieve low-cost liquid crystal display devices and to provide high-value added liquid crystal display devices as well as to achieve a wide viewing angle and high image quality. In addition, as high-value added liquid crystal display devices, the development for low power consumption has also been underway.
In order to improve viewing angle characteristics of liquid crystal display devices, in a liquid crystal display device which performs display by aligning liquid crystal molecules in a gradient manner or a radical gradient manner, it is disclosed that one pixel is divided into a plurality of independent pixel regions and different signals are added to each divided pixel region in each given period (for example, see Patent Document 4).
Further, as a method for satisfying basic display quality such as brightness and contrast and achieving sufficient low power consumption, a driving method of a display device in which a scanning period and a non-scanning period longer than the scanning period are set is disclosed (see Patent Document 5). Specifically, it is a driving method of a display device in which all data signal lines are electrically disconnected from a data signal driver in a break period in which all scan lines and data signal lines are in a non-selection state, so that a high impedance state is obtained.